Theodilite set up errors 1

[LordBerkley]

Can anyone explain why when setting up a theodolite you should not sight control points that are on a direct line between each other and the theodolite, i.e CP1 = 0^o and CP2 = 180^o.

I know doing this is likely to result in an error, but im struggling to work out why.

Any advice much appreciated.

LB

 

[IRstuff]

Seems to me that you would only be checking tilt in one horizontal axis, but not the other, since that would be a roll error that wouldn't be detectable.

TTFN
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[coloeng]

When setting up the theodolite using two known points to establish your location you are using triangulation to establish the point you are setting up on. If you use two points that are 180 degrees apart, you don't know where on the line between them your setup point is. The most optimum is to use two known points that are 90 degrees apart.